High School Trigonometry/Half-Angle Identities

$$\sin^{2}{u} = \frac{1 - \cos{2u}}{2}$$ $$\cos^{2}{u} = \frac{1 + \cos{2u}}{2}$$ $$\tan^{2}{u} = \frac{1 - \cos{2u}}{1 + \cos{2u}}$$